Yttria sintered body and corrosion-resistant material, and manufacturing method

ABSTRACT

The object of the present invention is to provide an yttria (Y 2 O 3 ) sintered body having high density and excellent plasma-resistance. The yttria sintered body has a structure in which a Y 2 O 3  crystal and a Y 3 BO 6  crystal are included as the constituent crystal thereof. In order to produce the yttria sintered body, a boron oxide (B 2 O 3 ) of 0.02 wt % to 10 wt % is added to an yttria (Y 2 O 3 ) powder, the mixed powder is formed, and thereafter sintered at 1300-1600° C.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an yttria sintered body which has low sintering temperature and excellent plasma-resistance.

2. Description of Prior Art

It is known that an yttria (Y₂O₃) has excellent plasma-resistance. Also, Patent Document 1-9 and Non-patent Document 1 have proposed that the density and the plasma-resistance of an yttria sintered body (Y₂O₃) are improved.

Patent Document 1 has proposed that a yttria (Y₂O₃) powder is formed by a cold isostatic press (CIP), the formed body is fired at 1400-1800° C., cooled, and thereafter heated at 1400-2000° C. in the presence of a boron compound (B₂O₃), so that a dense yttria (Y₂O₃) sintered body can be obtained. According to Patent Document 1, it is assumed that the dense sintered body can be obtained because the presence of a boron compound promotes sintering due to diffusion of a B₂O₃ inside the body.

Patent Document 2 has proposed that Si of 400 ppm or less and Al of 200 ppm or less are contained in an yttria to obtain an yttria sintered body having excellent plasma-resistance.

Patent Document 3 has proposed that Zr, Si, Ce or Al is used as a sintering aid to obtain an yttria sintered body having excellent plasma-resistance whose relative density is 95% or more, which cannot be achieved by a conventional technique.

Patent Documents 4-6 have disclosed that an yttria (Y₂O₃) sintered body having an excellent transparency and a mechanical strength can be obtained by a HIP treatment after hot pressing of an yttria (Y₂O₃) powder. Specifically, according to Patent Document 4, a lithium fluoride or a potassium fluoride is added as a sintering aid. According to Patent Document 5, a lanthanoid oxide is added as a sintering aid. According to Patent Document 6, the specific surface area (BET value) of an yttria (Y₂O₃) powder is adjusted to be 2 m²/g-10 m²/g.

Patent Document 7 has disclosed that Si of 200 ppm or less and Al of 100 ppm or less are contained in an yttria, and that Na, K, Ti, Cr, Fe, and Ni are adjusted to be 200 ppm or less, respectively, which is similar to Patent Document 2.

Patent Document 8 has disclosed that an yttria (Y₂O₃) green body or an yttria aluminum garnet green body having an excellent plasma-resistance is fired at 1650-2000° C. in a reducing atmosphere.

Patent Document 9 has proposed that a corrosion-resistant ceramic material used for an area to be exposed to plasma comprises an yttrium oxide, an aluminum oxide and a silicon oxide.

Non-patent Document 1 has disclosed that an yttria (Y₂O₃) powder is formed by a CIP (140 MPa), first sintering is performed to the formed body at 1400-1700° C., BN is sprayed on the sintered body, and second sintering is performed by a HIP (140 MPa, 1400-1700° C.), so that an yttria (Y₂O₃) sintered body having excellent transparency can be obtained.

Patent Document 1: Japanese Patent Application Publication No. 2000-239065

Patent Document 2: Japanese Patent Application Publication No. 2003-55050

Patent Document 3: Japanese Patent Application Publication No. 2001-181042

Patent Document 4: Japanese Patent Application Publication No. H04-59658

Patent Document 5: Japanese Patent Application Publication No. H04-238864

Patent Document 6: Japanese Patent Application Publication No. H04-74764

Patent Document 7: Japanese Patent Application Publication No. 2002-255647

Patent Document 8: Japanese Patent Application Publication No. 2003-48792

Patent Document 9: Japanese Patent Application Publication No. 2001-31466

Non-patent Document 1: Production of Transparent Yttrium Oxide by HIP sintering, The Ceramic Society of Japan, 2004, Preprint 2G09

Among these Documents, Patent Document 1 and Non-patent Document 1 disclose the closest technique to the present invention. Hereinafter, the details of Patent Document 1 and Non-patent Document 1 will be described.

Patent Document 1 discloses that heat treatment (HIP) is performed at 1400-2000° C. in the presence of a boron compound such as B₂O₃. Non-patent Document 1 discloses that a BN is sprayed, and second sintering is performed by a HIP at 1400-1700° C., so as to obtain an yttria (Y₂O₃) sintered body having a excellent transparency. Patent Document 1 also describes that even if the boron compound is not a B₂O₃, it is oxidized to be B₂O₃ by heating in an oxygen atmosphere or by bonding to an oxygen which is present on the surface of the fired body even in a case of heating in a no-oxygen atmosphere.

However, according to these documents, firing at relatively high temperature is required to obtain a sintered body having a small porosity, or a complicated manufacturing process such as a heat treatment in the presence of a boron compound after first sintering or a HIP treatment is required in order to obtain an yttria sintered body.

The object of the present invention is to provide an yttria (Y₂O₃) sintered body and a corrosion-resistance material having a high density and a excellent plasma-resistance which can be manufactured easily at low temperature, and a manufacturing method thereof.

SUMMARY OF THE INVENTION

The present inventors have been aware that the addition amount of B₂O₃ is very important to produce an yttria (Y₂O₃) sintered body by their researches. The results of the experiments the present inventors made show that when the addition amount of a B₂O₃ is large, a Y₃BO₃ phase appears, and when the addition amount of a B₂O₃ is small, a Y₃BO₆ phase appears. If a YBO₃ phase is included in a sintered body, the effect of increasing the density can be achieved at lower temperature than a case of Y₂O₃ alone, however, a sintered body having a high density cannot be obtained. On the other hand, if a Y₃BO₆ phase is included, the density can be increased sufficiently.

Therefore, an yttria sintered body according to the present invention is obtained by adding a boron compound to an yttria (Y₂O₃) powder and firing, and characterized in that a boron (B) is present in the yttria sintered body substantially as a Y₃BO₆. The preferred amount of the Y₃BO₆ in the yttria sintered body is 0.12 vol % to 60 vol %.

In order to produce the above-described an yttria sintered body, a boron oxide (B₂O₃) powder of 0.02 wt % to 10 wt % is added to an yttria (Y₂O₃) powder, the mixed powder is formed, and thereafter sintered at 1300-1600° C., preferably at 1400-1500° C.

A corrosion-resistant material according to the present invention is used for a substrate processing apparatus, and characterized in that a Y₂O₃ crystal and a Y₃BO₆ crystal are included in the corrosion-resistant material as the constituent crystal thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the relationship between firing temperature and relative density corresponding to an addition amount of a B₂O₃;

FIG. 2( a) is a SEM photograph in a case of no-addition and firing at 1300° C., FIG. 2( b) is a SEM photograph in a case of no-addition and firing at 1500° C., and FIG. 2( c) is a SEM photograph in a case of no-addition and firing at 1700° C.;

FIG. 3( a) is a SEM photograph in a case of 0.1 wt % addition and firing at 1200° C., and FIG. 3( b) is a SEM photograph in a case of 0.1 wt % addition and firing at 1400° C.;

FIG. 4( a) is a SEM photograph in a case of 1 wt % addition and firing at 1200° C., FIG. 4( b) is a SEM photograph in a case of 1 wt % addition and firing at 1300° C., FIG. 4( c) is a SEM photograph in a case of 1 wt % addition and firing at 1400° C., and FIG. 4( d) is a SEM photograph in a case of 1 wt % addition and firing at 1500° C.;

FIG. 5( a) is a SEM photograph in a case of 3 wt % addition and firing at 1200° C., and FIG. 5( b) is a SEM photograph in a case of 3 wt % addition and firing at 1400° C.;

FIG. 6( a) is a SEM photograph in a case of 10 wt % addition and firing at 1200° C., FIG. 6( b) is a SEM photograph in a case of 10 wt % addition and firing at 1300° C., FIG. 6( c) is a SEM photograph in a case of 10 wt % addition and firing at 1400° C., and FIG. 6( d) is a SEM photograph in a case of 10 wt % addition and firing at 1500° C.;

FIG. 7( a) is a SEM photograph of a fracture surface of a 0.1 wt % B₂O₃ addition system, and FIG. 7( b) is a SEM photograph of a specular surface in a state where thermal etching has been performed;

FIG. 8( a) is a SEM photograph of a fracture surface of a 1 wt % B₂O₃ addition system, and

FIG. 8( b) is a SEM photograph of a specular surface in a state where thermal etching has been performed;

FIG. 9( a) is a SEM photograph of a fracture surface of a 3 wt % B₂O₃ addition system, and FIG. 9( b) is a SEM photograph of a specular surface in a state where thermal etching has been performed;

FIG. 10 is an X-ray diffraction profile of a 0.02 wt % B₂O₃ addition system;

FIG. 11 is an X-ray diffraction profile of a 1 wt % B₂O₃ addition system;

FIG. 12 is an X-ray diffraction profile of a 10 wt % B₂O₃ addition system;

FIG. 13 is a graph showing the relationship between the amount of Y₃BO₆ in an yttria sintered body and the addition amount of boron oxide according to the present invention; and

FIG. 14 is a graph comparing plasma-resistance between the present invention and a conventional art.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An yttria (Y₂O₃) powder (RU: manufactured by Shin-Etsu Chemical Co., Ltd.) and a boron oxide (B₂O₃) powder (reagent-grade: manufactured by Junsei Chemical Co., Ltd.) were prepared as raw powders. 8 kinds of samples were prepared by adding no boron oxide (B₂O₃) powder to the yttria (Y₂O₃) powder, and adding the boron oxide (B₂O₃) powder to the yttria (Y₂O₃) powder at a ratio of 0.02 wt %, 0.1 wt %, 1 wt %, 3 wt %, 10 wt %, 16 wt %, and 23.6 wt %, respectively, and thereafter firing was performed at a firing furnace.

FIG. 1 shows the relationship between the firing temperature and the obtained relative density. FIG. 1 demonstrates the following:

In the case of adding no boron oxide (B₂O₃) powder, the temperature reached 1700° C., and a sintered body having relative density of about 95% was obtained. These firing temperature and relative density correspond to a known value.

Almost the same results were confirmed with respect to the cases of adding the boron oxide (B₂O₃) at a ratio of 0.1 wt %, 1 wt %, and 3 wt %. Specifically, the relative density started increasing at about 1000° C., and the relative density of more than 95% was obtained at 1400-1500° C. In particular, the relative density was almost 100% in the case of adding the boron oxide (B₂O₃) at a ratio of 3 wt %. It is assumed that sintered bodies having higher density were obtained in these cases than in the case of adding no boron oxide (B₂O₃) because a Y₃BO₆ produces a liquid phase in the firing process so as to cause a liquid-phase sintering.

Also, in the cases of adding the boron oxide (B₂O₃) at a ratio of 0.1 wt %, 1 wt %, and 3 wt %, the sintered bodies disintegrated at around 1583° C. It is assumed that disintegration occurs at this temperature because the boiling point of a Y₃BO₆ is around this temperature.

In the case of 10 wt %, it was confirmed that the relative density became high at 1300-1500° C. It is assumed that the density became high because slightly included a YBO₃ disappeared due to evaporation or decomposition as the temperature increased so as to turn a Y-B compound into a single phase of a Y₃BO₆.

In this way, a sintered body having high density can be obtained at relatively low temperature (1300° C. or more and less than 1600° C.).

In the cases of 16 wt % and 23.6 wt %, the relative density hardly increased, and the sintered body disintegrated at about 1500° C. It is assumed that a boron (B) became a YBO₃ phase and the YBO₃ phase underwent evaporation or decomposition.

FIG. 2( a) is a SEM photograph in the case of no-addition and firing at 1300° C., FIG. 2( b) is a SEM photograph in the case of no-addition and firing at 1500° C., and FIG. 2( c) is a SEM photograph in the case of no-addition and firing at 1700° C. In the case of no-addition, densification did not occurred at 1500° C., and a solid-phase sintering occurred at 1700° C.

FIG. 3( a) is a SEM photograph in the case of 0.1 wt % addition and firing at 1200° C., and FIG. 3( b) is a SEM photograph in the case of 0.1 wt % addition and firing at 1400° C. Densification occurred at 1400° C. in this case.

FIG. 4( a) is a SEM photograph in the case of 1 wt % addition and firing at 1200° C., FIG. 4( b) is a SEM photograph in the case of 1 wt % addition and firing at 1300° C., FIG. 4( c) is a SEM photograph in the case of 1 wt % addition and firing at 1400° C., and FIG. 4( d) is a SEM photograph in the case of 1 wt % addition and firing at 1500° C. The structure drastically changed at 1400° C. in this case.

FIG. 5( a) is a SEM photograph in the case of 3 wt % addition and firing at 1200° C., and FIG. 5( b) is a SEM photograph in the case of 3 wt % addition and firing at 1400° C. Densification occurred at 1400° C. in this case as well as in the case of 0.1 wt % addition.

FIG. 6( a) is a SEM photograph in the case of 10 wt % addition and firing at 1200° C., FIG. 6( b) is a SEM photograph in the case of 10 wt % addition and firing at 1300° C., FIG. 6( c) is a SEM photograph in the case of 10 wt % addition and firing at 1400° C., and FIG. 6( d) is a SEM photograph in the case of 10 wt % addition and firing at 1500° C. The structure drastically changed at 1400° C. in this case.

FIG. 7( a) is a SEM photograph of a fracture surface of the 0.1 wt % B₂O₃ addition system, FIG. 7( b) is a SEM photograph of a specular surface in a state where thermal etching has been performed, FIG. 8( a) is a SEM photograph of a fracture surface of the 1 wt % B₂O₃ addition system, FIG. 8( b) is a SEM photograph of a specular surface in a state where thermal etching has been performed, FIG. 9( a) is a SEM photograph of a fracture surface of the 3 wt % B₂O₃ addition system, and FIG. 9( b) is a SEM photograph of a specular surface in a state where thermal etching has been performed. These SEM photographs show that there is little Y₂O₃ grain growth because the firing temperature of the yttria sintered body is low.

If grain growth proceeds so as to make grains larger, the grains will be disjoined and the plasma-resistance will be deteriorated. However, according to the present invention, it is possible to control grain growth, so that a sintered body having a good plasma-resistance can be obtained.

FIG. 10 is an X-ray diffraction profile of the 0.02 wt % B₂O₃ addition system. This graph shows that slight Y₃BO₆ was slightly observed with a Y₂O₃ in the case of the 0.02 wt % B₂O₃ addition system.

FIG. 11 is an X-ray diffraction profile of the 1 wt % B₂O₃ addition system. This graph shows that a more amount of Y₃BO₆ was observed in the case of the 1 wt % B₂O₃ addition system than in the case of the 0.02 wt % B₂O₃ addition system.

FIG. 12 is an X-ray diffraction profile of the 10 wt % B₂O₃ addition system. This graph shows that slight YBO₃ was observed with a Y₃BO₆ in the case of the 10 wt % B₂O₃ addition system. It is assumed that when the addition amount of B₂O₃ exceeds 9.6 wt %, YBO₃ appears and the density becomes difficult to increase.

Next, the ratio of the Y₃BO₆ in the sintered body was calculated in the following manner:

An Y₂O₃ powder and a B₂O₃ powder were mixed such that a B₂O₃ was added at a larger ratio than a stoichiometric ratio for obtaining a Y₃BO₆ (9.3 wt %), pressed, and fired in a crucible under atmospheric pressure at 1400° C. for 10 hours. This was crushed, a B₂O₃ was added, pressed, fired in a crucible under atmospheric pressure at 1400° C. for 10 hour, and crushed again. It turned out that the obtained powder was a single phase of a Y₃BO₆ in which neither a Y₂O₃ nor a B₂O₃ existed by an XRD. The single phase of a Y₃BO₆ was confirmed based on the fact that it corresponded to JCPDS card 34-0291.

Reference samples were prepared by uniformly mixing the Y₃BO₆ powder obtained in the above-described manner (specific gravity: 4.638 g/cm³) and an Y₂O₃ powder (specific gravity: 5.031 g/cm³) at a volume ratio of 1, 5, 10, 20, 50 and 75 vol %, respectively. The mixed powder was measured by an XRD. The ratio of the value I_(Y2O3) obtained by adding the diffraction peak intensity of (khl)=(211), (400) and (440) and the value I_(Y3BO6) obtained by adding the diffraction peak intensity of (khl)=(003), (−601) and (−205) was calculated with respect to each XRD profile measured in the above-described manner. When I_(Y3BO6)/(I_(Y2O3)+I_(Y3BO6)) was set y-axis and the amount of Y₃BO₆ was set x-axis based on the calculated value, a linear relationship was obtained and this was used as a calibration curve.

FIG. 13 shows the results of checking the relationship between the amount of a Y₃BO₆ in the yttria sintered body and the addition amount of a B₂O₃ according to the present invention. When the B₂O₃ of 0.02-10 wt % was added, the amount of a Y₃BO₆ in the yttria sintered body was around 0.12-60 vol % although it depended on the atmosphere during the firing. It turned out that almost half boron evaporated during the firing.

With this, it is possible to densify an yttria sintered body at low temperature when the amount of a Y₃BO₆ in the yttria sintered body exceeds 0.12 vol % after sintering. Further, it is possible to obtain a stable sintered body having high density because a YBO₃ is hard to form and firing at low temperature is possible when the amount of a Y₃BO₆ in the yttria sintered body is less than 60 vol % after sintering.

As the boron compound, a boric acid (H₃BO₃), a boron nitride (BN) or a boron carbide (B₄C) may be used as well as a boron oxide (B₂O₃). Among these, the boron oxide and the boric acid are preferred.

FIG. 14 is a graph comparing the plasma-resistance between the present invention and a conventional art, and Table 1 also compares the plasma-resistance between the present invention and a conventional art.

TABLE 1 Comparative Comparative Present Example 1 Example 2 invention Material Y₂O₃ Sapphire Y₂O₃—Y₃BO₆ Corrosion Depth 300-400 1600 300-400 (nm) Average Corrosion 350 1600 350 Depth (nm) Ra before plasma 7.2 4 radiation (nm) Ra after plasma 15.4 9.8 radiation (nm)

FIG. 14 and Table 1 show that the yttria sintered body according to the present invention is excellent in plasma-resistance.

The yttria (Y₂O₃) sintered body according to the present invention can be used as a corrosion-resistant material which requires plasma-resistance such as a chamber, a capture ring, a focus ring, an electrostatic chuck of a plasma processing apparatus.

According to the present invention, it is possible to obtain an yttria (Y₂O₃) sintered body having high density and excellent plasma-resistance easily at relatively low temperature. 

1. An yttria sintered body obtained by adding a boron compound to an yttria (Y₂O₃) powder and firing, wherein a boron (B) is present in the yttria sintered body substantially as a Y₃BO₆.
 2. The yttria sintered body according to claim 1, wherein the amount of a Y₃BO₆ in the yttria sintered body is 0.12 vol % to 60 vol %.
 3. A corrosion-resistant material used for a substrate processing apparatus comprising a Y₂O₃ crystal and a Y₃BO₆ crystal as the constituent crystal thereof. 